Western Australia in January 2013: A hot month for WA

Rainfall

Rainfall during January 2013 was above- to very-much-above-average
through much of western and central WA, but particularly in central and western
parts of the Pilbara as a result of local thunderstorm activity as well as the
passage of tropical cyclone Peta through the region bringing some record
daily falls. Western parts of the Gascoyne also saw above average rainfall due
to local thunderstorm activity, as did northern parts of the Southwest Land
Division (SWLD) as a cloudband associated with tropical cyclone Narelle
brought some heavy falls. Below average rainfall was mainly confined to parts
of the Kimberley and northeast Southern Interior as monsoonal activity was confined
to a brief period in the middle of the month with the majority of rainfall a
result of diurnal shower and thunderstorm activity.

Averaged across the state as a whole, rainfall during
January 2013 was close-to-average for WA, while for the Lower Southwest (southwest
of a line from Jurien Bay to Bremer Bay) and the SWLD January 2013 rainfall
was above average.

Although a short-lived weak system, tropical cyclone
Peta moved across the Pilbara coast near Roebourne on the afternoon of
the 23rd and weakened to a tropical low. It brought significant rainfall to
eastern coastal and central inland parts of the Pilbara from the 20th to the
25th with numerous daily falls over 100 mm reported. The highest daily fall
during the event was 261.6 mm at Hooley on the 24th, which was the highest daily
rainfall in WA for the month, and the wettest day at Hooley in 29 years of record.
Mount Florance recorded 220.0 mm also on the 24th, its wettest January day in
106 years of record, whilst the following day Wittenoom recorded 228.0 mm, its
highest daily fall in January in 58 years of record. Between 0900 WST on 22nd
and 0900 WST on 25th, Hooley, Wittenoom, and Mount Florance all reported over
300 mm, with Hooley recording the highest total of 377.0 mm. Flooding impacts
were generally localised and mostly minor.

Tropical cyclone Narelle moved southward parallel
with the WA west coast from the 12th to the 15th and weakened into a low as
a cloudband associated with the tropical low, and consequent thunderstorm activity
due to increased atmospheric moisture, brought unseasonal rainfall to western
and southern parts of the State. The highest daily falls were in the 50 mm to
100 mm range in the Central West, Central Wheat Belt, and Goldfields. This event
brought the majority of Kellerberrin's January rainfall total of 104.3 mm, and
was the main reason for the site recording its wettest January in 119 years
of recording.

Maximum temperature

Maximum temperatures during January 2013 were above- to very-much-above-average
over much of western, southern, and eastern WA, as well as large parts of the
Kimberley, with daytime temperatures up to 4 °C above normal in the
eastern Southern Interior, as well as in the Shark Bay area of the west Gascoyne.
Below average maxima were confined to the Pilbara, due to the relatively wet
and cloudy month, with daytime temperatures to 2 °C below normal in
central and western parts of the district.

When averaged across the state as a whole, the mean maximum temperature for
WA for January 2013 was well above average and ranked eleventh-highest since
comparable records commenced in 1910, continuing the run of above average monthly
mean maxima for WA since April 2012. When averaged across the Lower Southwest
(southwest of a line from Jurien Bay to Bremer Bay), the mean maximum temperature
was above average.

January 2013 began with very hot conditions in southern and southeast WA on
the 1st as the trough near west coast moved eastward, and temperatures reached
the low-to-mid forties. The hot conditions shifted to the southeast corner of
WA on the 2nd and 3rd and intensified as the trough moved slowly eastward. Eucla
recorded a daily maximum temperature of 48.2 °C on the 3rd, which exceeded
the previous highest January temperature at the site in its 51 years of record
of 47.9 °C on 3 January in 1979. Red Rocks Point (west of Eucla) registered
48.6 °C on the same day, which was the highest temperature at that site
in its 9 years of record, and the highest temperature recorded in the Eucla
district in almost 31 years, since Mundrabilla Station recorded a maximum temperature
of 48.6 °C on 15 February 1983. Exceptional conditions were also experienced
in the inland Gascoyne, northern Goldfields, and Northern and Southern Interior
from the 7th to the 10th as a very hot airmass lay over the region with clear
skies and light winds. A number of sites recorded their hottest January day
on record multiple times during this period, including Paynes Find, Yeelirrie,
Wiluna, and Meekatharra Airport. Leonora in the Goldfields broke its previous
record of 47.8 °C twice, on the 8th (48.3 °C), and 9th (49.0 °C),
with the latter being the highest temperature of the month in WA. Giles Meteorological
Office in the Southern Interior saw four consecutive days with temperatures
above 44 °C between the 7th and 10th, and in its 57 years of record had
only recorded consecutive days over 44 °C once before, on 1 and 2 January
1973. Giles twice broke its all-time record temperature during this spell but
high temperatures returned from the 13th to 17th and a daily maximum temperature
of 45.7 °C on the 16th became the new record high for the site. Partly as
a result of these hot spells, Giles Meteorological Office recorded its equal
highest January mean maximum temperature with 40.3 °C, only 0.1 °C behind
its hottest month on record; February 2007. Ongerup in the South Coastal also
recorded its equal warmest January on record.

Minimum temperatures

Minimum temperatures during January 2013 were above- to very-much-above-average
across most of the State, with areas of highest on record in the Great Southern,
South and Southeast Coastal as several sites recorded their warmest or equal
warmest January on record. Overnight temperatures were up to 5 °C above
average in the southeast Northern Interior, north of Giles. In contrast, parts
of the southeast Pilbara and eastern Gascoyne recorded below average overnight
temperatures with mean minima 2 °C to 3 °C below normal in the
east Gascoyne.

When averaged across WA as a whole, the mean minimum temperature during January
2013 was well above average and ranked as the third-warmest January on record.
This continues a recent very warm trend for WA January minimum temperatures
with the warmest five Januarys being 2011 (1st), 2008 (2nd), 2013 (3rd), 2010
(4th), 2009 (5th) from comparable temperature records commencing in 1910. The
Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay) also saw
well above normal overnight minima, with the region observing its eighth-warmest
January, continuing a run of above average January mean minima for the region
with 2012 being the warmest on record and 2011 fifth-warmest.

Very warm nights were reported across southern WA to start the month and Cape
Leeuwin in the Southwest recorded a daily minimum temperature of 23.8 °C
on the 1st, breaking its previous warmest January night in 107 years of record
of 23.5 °C set on 26 January 2012.Very warm
nights were reported across much of WA between the 6th and 10th and several
sites in the Southwest district reported record high minima on the 8th, along
with Merredin in the Central Wheat Belt and Paynes Find in the southern Gascoyne.
Cape Leeuwin reported a minimum of 24.2 °C, again exceeding its January
record. Wiluna recorded an overnight temperature of 33.5 °C on the 9th,
the highest minimum temperature of the month for WA. Very warm nights were again
experienced in much of WA between the 15th and 17th and Perth Airport recorded
its highest January minimum in 69 years of record on the 15th with 27.8 °C,
whilst Albany Airport recorded a minimum of 20.9 °C, almost 1 °C above
its previous January record. Large parts of WA welcomed cooler than normal nights
in the last week of January.

Tropical Cyclones

Severe tropical cyclone Narelle formed well north of the Australian
coast on the 8th and took a general southwesterly track, intensifying to a category
four system on the 11th north-northwest of Exmouth. Narelle moved south-southwest
off the WA west coast and was downgraded to a low early on the 15th, over 500
km to the west of Geraldton. Although threatening the Pilbara and Gascoyne coasts
and disrupting shipping and offshore industries, Narelle remained far
enough offshore not to directly impact the northwest coast. A tidal surge was
recorded from Onslow to Busselton as a result of Narelle causing some
inundation of low lying areas, though any impacts were minor.

A tropical low formed over in the Kimberley on the 20th and tracked southwest
through the west Kimberley then close to and parallel with the Pilbara coast
before turning to the southwest towards the Pilbara coast early on the 23rd.
The system intensified into tropical cyclone Peta (category 1) on the morning
of the 23rd and crossed the coast near Roebourne then weakened to a tropical
low in the afternoon on the 23rd. Although tropical cyclone Peta was short-lived
and relatively weak, its proximity to the coast resulted in disruptions to shipping
and offshore industries. There was also significant rainfall along parts of
the Pilbara coastline and in the Fortescue catchment, with accumulated falls
over 300 mm reported, leading to minor flooding.

Notes

A Monthly Climate Summary is prepared to list the main features of the weather in Western Australia using the most timely and accurate information available on the date of publication; it will generally not be updated. Later information, including data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review, usually published in the fourth week of the month.

This statement has been prepared based on information available at
10 am on Friday 1 February 2013.
Some checks have been made on the data, but it is possible that results will change
as new information becomes available.

Averages are long-term means based on observations from
all available years of record, which vary widely from site to site.
They are not shown for sites with less than 10 years of record, as they cannot then be calculated reliably.
The median
is sometimes more representative than the
mean
of long-term average rain.

The Rank indicates how rainfall this time compares with the climate record for the site,
based on the
decile ranking
(very low rainfall is in decile 1, low in decile 2 or 3,
average in decile 4 to 7, high in decile 8 or 9
and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a
percentage of the long-term mean.

The ACORN-SAT dataset
is being used for temperature area averages from December 2012 onwards.
The major change from earlier datasets is that the ACORN-SAT dataset commences in 1910, rather than 1950,
and hence rankings are calculated using a larger set of years.